The bioautofuel cell will produce electrical power by direct conversion of chemical energy from endogenously supplied carbohydrate fuel and oxygen to usable electrical energy for implantable electronic devices such as the cardiac pacemaker. In addition to problems of fuel cell design, electrode and membrane materials, etc., the investigation involves the design and packaging of a microminiature pacemaker circuit and fuel cell, without leads, and theoretically capable of unlimited life. In its homeostatic processes, the body would be the ever faithful servant in providing fuel and oxidant (e.g. glucose and oxygen at their physiologic concentration in extracellular fluid). Because of construction with inert materials, the cell could continue to function for the life of the patient even in the case of implantation in childhood: certainly much longer than the present state-of-the-art pacemaker with mercury or other primary or secondary cells. Also under study are an entrapped enzyme reactor for processing of body fluid fuels, characterization of various potential fuels, identification of reaction products, appreciation of neutral pH, body temperature fuel cell kinetics and exploitation of the new power source for other applications such as carotid sinus nerve stimulation, urinary bladder stimulation and implantable biotelemetry systems. The fuel cell and its problems will be approached in the general context of the pacemaker requirements, but the work applies to other uses as well.